The present invention relates to a metal mold for resin molding which can mold a resin compact of uniform molding density, and more particularly to a metal mold for resin molding which can mechanically define a precise pressing mold gap by using guide post rods.
As a disk type information recording media, optical audio, and video and magnetooptics discs are known.
FIG. 1 is a sectional view of an example of such a disk type information recording medium.
Such disk type information recording media are made of transparent resin material of good light transmittivity and at the center of the disk there is formed an opening 1 with which the disk is mounted on a revolving shaft. The upper surface 2 of such disk type information recording media is finished to a mirror face having a surface coarseness within 0.01.about.0.02 micron meter, and extremely minute rugged pits for recording information are formed concentrically at the lower surface 3 thereof.
In the case of optical audio and video disks, laser spot light is irradiated downwardly from that upper surface 2 while rotating the disk, and the changes of light reflected by the rugged pits formed at the rear side 3 of the disk are taken out to read information. In the case of the magnetooptics disk, specific magnetic material is coated on both the upper and rear surfaces of the disk, the magnetic material being able to generate changes of phase in response to the laser spot light energy. The recording and erasing of information may therefore likewise be performed.
In the magnetooptics disk, high reliability of information is required, compared with that required in the optical audio disk or video disk. For example, as a standard of reliability, an example of the precision in the double refraction rate is now explained. In general, in the optical audio disk, an error of .+-.50 nm is allowable, while in the case of the magnetooptics disk, a precision within .+-.5 nm is required.
In order to improve the preciseness of the double refraction rate when manufacturing the magnetooptics disk by the injection molding of the transparent resin material, a method of improving the evenness of the molding density of a disk has been proposed.
FIG. 2 is a view for explaining the method for improving the molding density of the resin mold compact. In the figure, the final disk thickness to be obtained is given by t, as shown in the right-hand portion of the figure. At the time of injection for filling the resin material; the thickness of the cavity is first held at t1 made somewhat larger than t, and the resin material is injected with relatively low injection pressure and filled into the cavity space, as shown in the left-hand portion of FIG. 2. Then pressure is applied thereto for molding so as to obtain the final thickness t of the disk, as shown in the right-hand portion of FIG. 2.
FIG. 3 is a sectional view of an example of a conventional metal mold for resin molding, which may be press molded, left-hand portion of the figure representing the state of injection for filling the material and the right-hand portion representing the state where pressure is applied thereto.
In FIG. 3, the reference numeral 4 indicates a fixed plate, 5 a nozzle, 6 a movable plate, 7 a fixed metal mold plate, 8 guide post rods, 9 a passage for feeding the resin material and 10 a fixed side cavity plate. 11 is a stepped flat surface formed on the fixed side cavity plate 10, 12 a movable metal mold plate, 13 bores for guiding the guide post rods 8, 14 a movable side cavity plate and 15 an end flat surface of the movable side cavity plate 14.
The fixed plate 4 forms a part of an injection molding machine and is fixed to its body. The nozzle 5 is for injecting through it the melt resin material into the cavity and is movable axially. The fixed metal mold plate 7 is mounted to the fixed plate 4, and the guide post rods 8 are mounted to the plate 7. At the center of the plate 7 is mounted the passage 9 through which the melt resin material passes. At the outer periphery of the fixed side cavity plate 10 is formed the stepped flat surface 11. The fixed side cavity plate 10 is integrally mounted to the fixed metal plate 7 which is fixed to the fixed plate 4, and so these portions form a fixed side metal mold assembly.
The movable plate 6 moves in the axial direction to press and open the mold. The movable metal mold plate 12 is fixed on the movable plate 6, and in the plate 12 is formed the guide bores 13 for guiding the guide post rods 8. The movable side cavity plate 14 is integrally mounted to the movable side metal mold plate 14, and mates with the fixed side cavity plate 10 at the respective complementary peripheral surfaces of the plates 14 and 10. When the end surface 15 of the movable side cavity plate 14 fits pressedly with the stepped surface 11 of the cavity plate 10, a cavity space is formed to mold the compact whose thickness is t, corresponding to the final thickness of the pressed molding compact. The movable side cavity plate 14 is integrally mounted to the movable metal mold plate 12 which on the other hand is fixed to the movable plate 6, all of these elements forming a movable side metal mold assembly.
The press molding operation of the conventional resin molding metal mold shown in FIG. 3 is explained.
The movable plate 12 is at first opened and stopped for the press molding gap of t1-t, while an adequate pressing power is applied thereto so that it does not retreat any further even though subjected to the injection pressure. Melt resin material is then injected through the passage 9 to fill the cavity and obtain a compact, as shown in the left-hand portion of FIG. 3. The holding state of the movable metal mold is now released and the movable metal mold plate 12 is pressed and moved until the stepped surface 11 of the fixed side cavity plate 10 and the peripheral end surface 15 of the movable side cavity plate 14 are in contact with each other. Thus a compact of the final thickness t may be molded by applying pressure, as shown in the right-hand portion of FIG. 3.
In the case of the magnetooptics disk and other optical disks, the desired thickness t of the disk is 1.2 mm and the maximum press molding gap must be 10% or less of this thickness of the disk. In other words, for obtaining a gap of 0.12 mm or smaller thickness, the temporary holding position of the movable metal mold plate 12 must precisely be adjusted in the cavity plate for injection molding. Such requirements can not be satisfied when the articles are manufactured under a mass production basis. Further, even if the evenness in each compact may be improved, the evenness of the compacts on a large amount of compacts as in a lot can not be assured.
The shape and form of the compact itself is rather simple, but the requirements of the metal mold for the various information recording disks are very high. Further, various circuits, such the as cooling water circuit, hydraulic circuit, pneumatic circuit, vacuum suction circuit, pressure sensor, temperature sensor, signal stamper removable device, etc. are mounted to the metal mold. For this reason, there are many connecting portions between the metal mold and the body of the molding machine and portions thereof. For example, in the case of a metal mold for a magnetooptics disk of 130 mm in diameter, there are 32 such portions, and so the side surface of the metal mold are almost covered with these many portions. For this reason, it is not possible in such a metal mold to add the mechanics for adjusting the molding gap, which therefore requires mounting the metal mold to an unnecessarily larger apparatus for giving the function to the mold.
An object of this invention is therefore to provide a small sized resin molding metal mold, which can rather simply and mechanically adjust the press molding gap for a disk to be formed.